In the conventional liquid crystal display device of active matrix type, a plurality of scanning lines and a plurality of data lines are arranged to extend in a row direction and a column direction, namely mutually orthogonally, in a display area. A pixel electrode is arranged in each region surrounded with adjacent scanning lines and adjacent data lines and connected via a thin film transistor as a switching element to a scanning line and a data line.
In the liquid crystal display device described in JP H07-175453 A, a plurality of storage capacitance lines for forming storage capacitances with pixel electrodes are arranged so that each of the storage capacitance lines extends in the direction of a row, namely parallel to a scanning line. The storage capacitance lines are arranged in a common plane with the scanning lines and arranged to intersect with the data lines arranged in a plane different from this plane.
Explanation is made about a driving method of the conventional liquid crystal display device. Upon selecting a certain scanning line and applying a potential of high level to the selected scanning line, all the data lines are supplied with respective image signals to write the image signals in all the pixel electrodes connected via the thin film transistors to that scanning line. After the lapse of a constant selection time period, the potential on that signal line is reduced to low level. After that, the next scanning line is selected and the writing is likewise performed. Thereafter, such writings are repeated to write image information for one screen. Thus, to write image information for one screen, each of the scanning lines is selected (i.e., driven) only once while the data lines are driven numerous times corresponding to the number of the scanning lines.
The electric power consumption of the data lines for one screen is obtained by the [voltage amplitude]×[write capacitance to be driven]×[the number of times writing/driving operations are performed]. While the voltage amplitude on a data line (e. g., 5 volts) is one fifth to one seventh of the voltage amplitude of on a scanning line (e.g., 30 volts), the number of times the writing operation is performed on a data line is the number of the scanning lines (e.g., several hundreds), so that the power consumption at the data lines is considerably larger than the power consumption at the scanning lines.
In the conventional liquid crystal display device, because the storage capacitance lines overlap with the data lines, a parasitic capacitance is generated where the storage capacitance lines and data lines cross with each other. This parasitic capacitance presents a problem in that it is one of the causes of the increased power consumption at date lines.
Accordingly, an object of the present invention is to provide a display device that reduces the power consumption of data lines.